The inherent irregular motion and mutual repulsion of air molecules will form a static force, and this pressure is atmospheric pressure. Sound is the vibration of air molecules, and the vibrating air molecules will generate additional pressure on the section through which it passes. This additional pressure is called sound pressure. The sound pressure is much smaller than the atmospheric pressure. Generally, the sound pressure level is used to describe the size of the sound, that is, a small sound pressure p0=2 х10-5 Pa is used as the reference sound pressure, and the sound pressure to be measured p The ratio with the reference sound pressure p0 takes the common logarithm and multiplied by 20. The value obtained is called the sound pressure level, and the unit is decibel (db). The decibel (dB) is named after Bell, the American telephone inventor, because the unit of the decibel is too large, so the decibel is used, representing 1/10 of a decibel. The operation of decibels is not linear, but logarithmic. When using decibels to describe sounds, you need to give frequencies at the same time.
The working principle and composition of sound level meter
Sound level meter is the most basic instrument in noise measurement. It is generally composed of microphone, preamplifier, attenuator, amplifier, frequency weighting network and RMS indicator.
The working principle of the sound level meter is:
The sound is converted into an electrical signal by the microphone, and the impedance is transformed by the preamplifier to match the microphone and the attenuator. The amplifier adds the output signal to the weighting network, performs frequency weighting on the signal (or an external filter), and then amplifies the signal to a certain amplitude through the attenuator and amplifier, and sends it to the RMS detector (or external power supply). flat recorder), the value of the noise sound level is given on the indicator head.
